The vapor trapping canister vapor pressure management system relates to underground fuel storage tank vapor recovery, in general, and more specifically, to the capture and purging of hydrocarbon vapors as released from an underground storage tank during fueling by ORVR vehicles. A unique aspect of the present invention is retention of hydrocarbons in the vapor pressure management canister while allowing inflow and outflow of other gases to regenerate the carbon in the canister.
Fuel storage tanks, such as underground storage tanks, UST, used to store gasoline at gas stations, are subject to variable pressures that affect the ability of the fueling system and vapor recovery system to operate correctly. The fuel storage tanks thus have vents which release the excess pressure when the tank exceeds a certain predetermined maximum pressure. Excess pressure can be caused by vacuum assisted refueling as when more vapors are drawn into the tank than volume of fuel dispensed, by not connecting the vapor return hose to the transfer tank when refueling the tank, or by local atmospheric conditions, particularly barometric pressure changes associated with weather fronts. Additionally, negative pressure or partial vacuums can appear in the storage tank by dispensing more fuel than vapors that are drawn into the tank as during vacuum assist, or balance system, refueling. In that situation, the tank requires additional pressure or more likely the vacuum must be dissipated.
Since the 1998 automotive model year, onboard refueling vapor recovery, ORVR, technology has been employed initially on passenger cars and presently on light trucks. As is well known, the motorist refuels his/her vehicle at a service station. The fuel is pumped from an underground tank, by the dispenser, through a hose and nozzle, for filling the vehicle fuel tank. Normally, the vapors generated within the fuel tank, through refueling, are returned through the vapor path of the fuel hose, back to the dispenser, either by the balanced pressure method—called Stage II vapor recovery—or by a pump, and then are returned to the underground storage tank for containment.
Escaped gasoline vapors raise pollution concerns and trigger governmental regulations. Hydrocarbon vapors, such as octane, under the action of sunlight form ground level ozone. Such ozone affects the respiratory tract in humans. Normally, balance type Stage II vapor recovery stations operate at a negative pressure except during closure of the station. When an ORVR equipped vehicle is refueled, the ORVR system retains the vapors from the vehicle fuel tank, and does not return the vapors to the dispensing system, often lowering the pressure within the fuel storage tank. An ORVR vehicle refueling at a Stage II equipped station imposes a negative pressure on the Stage II system that draws atmospheric air into an underground fuel tank. The atmospheric air then absorbs hydrocarbons from stored fuel and with each ORVR vehicle that refuels, the pressure in the underground tank increases. When that pressure exceeds a limit, valves release the air containing hydrocarbons from the tank to the atmosphere thus, contributing to pollution when attempting not to do so.
Generally, various methods capture gasoline vapors and then return them to the underground tank. In doing so, the vapor recovery systems prevent vapors from escaping to the atmosphere as components of pollution. Vapor recovery systems are of two types. First, the vacuum assist system utilizes the partial vacuum created within the nozzle, by means of the flowing fuel passing through the nozzle during its dispensing, or a vacuum pump, and this partial vacuum tends to attract vapors back into the nozzle, either through a bellows arrangement used in conjunction with the nozzle spout, or through a passage created between concentrically arranged nozzle spouts, that allows the partial vacuum to attract the vapors back into the spout for return to the underground storage tank. Second, the balanced pressure system begins upon pumping gasoline in an automobile fuel tank, then displaced air is forced back towards the emplaced nozzle and that forces the gasoline vapors to be captured for return back into the fuel line, and eventually back to the underground storage tank.
Prior art designs defeat pressurization and vapor absorption in the underground fuel tank by two classes of devices. First, nozzles and other parts of the dispensing system are regulated by an ORVR detecting sensor. The sensor recognizes the pressure dip caused by an ORVR vehicle and promptly reduces air ingestion to less than the volume of fuel dispensed. The sensor and nozzles result in a slight negative pressure in the underground tank that limits vapor loss to the atmosphere. Second, membranes and condensing processes control the vapor at the source, in the underground fuel tank. The membranes and condensing processes cool or otherwise liquefy gasoline vapors and return them to the underground tank while letting cleansed air return to the atmosphere. Though collecting vapors, the prior art required additional mechanical equipment, and has higher installation and operational costs, and energy consumption.
The patent to Healy, U.S. Pat. No. 5,305,807, describes a vapor recover device. This device has a vacuum pump connected to underground storage tanks coupled with a solenoid. A pressure switch monitors pressure in the UST and energizes the solenoid to move valves within three conditions to direct air flow into or out of the UST. The valves control flow of hydrocarbons and air through a conduit system. This patent discloses a pump and solenoid not in the present invention.
The present art overcomes the limitations of the prior art. That is, the present invention, a vapor trapping canister vapor pressure management system, provides containment and purging of hydrocarbons in fuel vapors while allowing passage of air through the canister of the system. The canister system uses pressure differences created in the underground tank by ORVR vehicles to move hydrocarbons into the canister and air out of the canister without active electrical or chemical means. In other words, no pumps are required.
Thus, prior art devices do not provide for purging hydrocarbons in a container and preventing their return into an underground fuel tank while allowing air to pass freely through the container. The present invention uses the weakness of the interaction between an ORVR vehicle and a stage 11 dispensing system to collect and purge hydrocarbon vapors while returning air alone to the atmosphere.